Means proportional to magnetic flux to bias electric switch contacts closed



31, 1968 R. c. BREMER I MEANS PROPORTIONAL T0 MAGNETIC FLUX T0 BIAS ELECTRIC SWITCH CONTACTS CLOSED Filed Dec 1a, 1966 F/GZ d w nmm w/w. M38 W MW a mw mfi. mm nw .e m V w W m United States Patent MEANS PROPORTIONAL TO MAGNETIC FLUX TO BIAS ELECTRIC SWITCH CONTACTS CLOSED Randall C. Bremer, East Granby, Conn., assignor to Arrow-Hart, Inc., Hartford, Conn., a corporation of Connecticut Filed Dec. 13, 1966, Ser. No. 601,382 Claims. (Cl. 335-16) ABSTRACT OF THE DISCLOSURE An electromagnetically operated contactor having one or more pairs of fixed contacts engaged and disengaged by a movable contact as the contactor is energized and deenergized, in combination with means to concentrate an electromagnetic flux field creating a force acting on the bridging contact tending to hold it closed on occurrence of heavy excess current conditions such as upon a direct short circuit, and tending to minimize contact bounce as the contacts engage under high in-rush current conditions, the force being in proportion to the square of the current.

BACKGROUND OF THE INVENTION In prior art electromagnetically operated contactors of the type to which this invention relates, the bridging contacts were routinely pressed against the fixed contacts by springs. However, a force created, such as upon the occurrence of a direct short circuit, often became strong enough to overcome the spring bias and move the bridging contact away from the fixed contact just at the time when the current was greatest, thus causing destructive arcing and burning of the contacts. Contactors are not designed to open the circuit on occurrence of overloads, such opening being the function of safety or overload devices designed particularly for interrupting the current flow on occurrence of overload. Various theories have been advanced of reasons for this acknowledged phenomenon, but no attempt is made to evaluate or choose between them here.

Also, in proir art contactors, it has long been known that the movable contacts would bounce on the fixed contacts when the contactor was energized to close it. This bounce had a deleterious eifect particularly when there was a high initial in-rush of current.

SUMMARY OF INVENTION According to this invention, the current path through the contactor is through a conductive member adjacent the contacts and through the contacts, all being arranged to create a current loop of U-shape. Within the loop, there is a concentration of the lines of electromagnetic flux creating a force in proportion to the square of the current acting on the movable contact in a direction to press it into engagement with the fixed contacts. This holds the contactor more firmly closed during excess or heavy current conditions. The greatest force is exerted under direct short circuit conditions, under which conditions prior contactors tended to open. A lesser, but nevertheless a strong force in addition to the biasing spring force acts on heavy current in-rush to prevent contact bounce such as occurred in prior contactors.

In the drawing:

FIG. 1 is a plan view of an electromagnetic contactor embodying the invention.

FIG. 2 is a side elevation view, partly in section, taken along the line 22 of FIG. 1.

FIG. 3 is a front elevation view of the contactor of FIGS. 1 and 2.

3,419,828 Patented Dec. 31, 1968 DETAILED DESCRIPTION Referring to the drawing, as in conventional electromagnetic contactors a substantially fiat rectangular metal base plate 10 has mounted perpendicularly on it a pair of parallel spaced side plates 12, 12' having in-turned top edges on which is mounted an insulating body or base 13.

In the area between the base 10, body 13 and plates 12, 12', known operating mechanism is mounted as in the H. E. Schleicher Patent 2,719,890, issued Oct. 4, 1955, to which reference may be had for description of the structure and operation of the operating mechanism of the sort illustrated herein. Generally speaking, a laminated field piece 15 has a movable laminated armature 16 cooperating therewith to move a transverse actuating bar 17 rectilinearly, the bar being guided in slots in the side plates 12.

A U-shaped stamped sheet metal movable contact carrier 19 has insulating posts 18 mounted on it, one for each pole of the contactor depending on the number of lines in the circuit in which the contactor is connected. The posts each extend upwardly through passageways in the base or body 13 and have mounted on the top thereof bridging contact members 23 in the form of fiat bars of metal possessing good electrical conductivity. Bridging contact 23 is adapted to engage and disengage a pair of contact buttons 22 mounted on fixed contact plates which may be in the form of narrow bars stamped from sheet metal. As the electromagnet of the contactor is energized and deenergized, the bridging contact is moved toward and away from the fixed contacts.

A coil spring 24 exerts pressure on the bridging contact when the contactor is energized to hold the bridging contact in engagement with the fixed contact resiliently.

The fixed contact plates are preferably, but not necessarily, seated in parallel channels in the upper surface of the insulating body 13, with opposite plates of the same line of the system in alignment. On one plate 20, a con ventional wire terminal 27 is mounted. The fixed and movable contacts are covered and protected by a hood of molded insulating material 25 secured by bolts over and upon the body 13. All the above described structure is known.

To provide a structure creating a concentration of the lines of force tending to hold the contacts in engagement, at flux concentrating member 30 is provided. It is stamped from sheet metal of good electrical conductivity in the form of a strip and is bent into the shape to be attached at one end to a contact plate, such as 21, preferably by a screw 31. From there, it passes through a channel molded in the insulating hood 25, then across the hood toward the opposite fixed contact plate 20, passing over the bridging contact 23 and its biasing spring 24 to a point near the wire terminal 27. At that point, the flux concentrating member is bent up and reversely and a conventional wire terminal member 32 is mounted thereon.

In the example shown, the flux concentrating member is bent in two steps, toward and over the bridging contact member 23 and biasing spring 24 and then down one step to the reversely bent portion on which the wire terminal 32 is mounted. However, this particular shape for the flux concentrating member is not essential. A curved or other shape may be satisfactorily employed, also, so long as there is a greater concentration of electromagnetic flux on the opposite side of the bridging contact than on the side on which the fixed contacts are located.

As will be seen in FIG. 4, the flux between the bridging contact 23 and the flux concentrating member 30 results from the lines of force of the electromagnetic field around the bridging contact plus the lines of force around the flux concentrating member 30. In other words, the path of current is through a U-shaped conductor, the conductor being composed of the fixed contacts 20 and 21 and bridging contact 23 and their contact buttons and then through the flux concentrating member 30. In consequence, there is a concentration of electromagnetic flux 34 which creates a force in the direction of the arrow B on the bridging contact. This force A tends to keep the bridging contact in engagement with the fixed contacts. Moreover, the force is increased as the square of the current increases and, thus, the force is stronger during the occurrence of a great overload, such as under direct short circuit conditions. Conversely, the force diminishes as the current drops off, as in normal due to the action of the usual safety devices put in the circuit for excess current interruption. Thus, the contactor may become deenergized and the bridging contact may separate from the fixed contacts under normal conditions rather than under abnormal conditions.

Not only is the force created on short circuit conditions, but it is created also upon a high current inrush as the contacts engage when the contactor is energized to close it. This force tends to minimize contact bounce on the occurrence of high current in-rush.

Thus, the invention acts most effectively and very advantageously when the current conditions are most severe and when they would be most likely to harm the contacts.

It is clear from the foregoing that the flux concentrating member 30 is or may be a wire terminal member configured to overlie the fixed and bridging contacts, and that it must be sufficiently rigid or rigidly supported in the arc hood so that the force of the concentrated flux field will not be dissipated by movement of the member 30 away from the movable contact 23. Obviously, the further away from the movable contact 23 the terminal and flux member 30 is placed, the weaker will be the fl-ux concentration force. Hence, it is desirable to place these members as close as the arc hood will permit while still affording adequate protection against arcing.

Many modifications Within the scope of the invention will occur to those skilled in the art. Therefore, the invention is not limited to the 'precise form and the configuration of parts as illustrated and described.

What is claimed is:

1. In combination with an electric switch having a pair of fixed contact members and a movable contact member adapted to engage and disengage said fixed contact members, and means resiliently pressing said movable contact member against said fixed contact members in engaged position, rigid current carrying means which is located in proximity to said movable contact to combine the electro magnetic field surrounding said rigid means and said movable contact creating a concentration of electromagnetic flux exerting pressure on said movable contact member toward engaged position, the pressure being in proportion to the square of the current passing through said fixed and movable contact-members.

2. The combination as claimed in claim 1 wherein said rigid conductive member is connected with one of said fixed contact members and overlies said movable contact member and carries the same current as said movable and fixed contact members.

3. The combination as claimed in claim 1 wherein said rigid means includes a rigid wire terminal member connected with one of said fixed contact members and configured to overlie said movable contact member and said resilient means, whereby the current entering through the other fixed contact member passes through the movable contact and said onecontact member and said terminal member.

4. The combination as claimed in claim 2 having an insulating arc hood over said fixed and movable contact members, said conductive member overlying said hood on the opposite side thereof from said contact members.

5. The combination as claimed in claim 3 in combination with means providing an insulation shield between said wire terminal member and said contact members.

References Cited US. Cl. X.R. 

